Clear-text protocols such as ftp, telnet or non-secure http lack encryption of transported data, as well as the capability to build an authenticated connection. It means that an attacker able to sniff traffic from the network can read, modify or corrupt the transported content. These protocols are not secure as they expose applications to an extensive range of risks:

Even in the context of isolated networks like offline environments or segmented cloud environments, the insider threat exists. Thus, attacks involving communications being sniffed or tampered with can still happen.

For example, attackers could successfully compromise prior security layers by:

In such cases, encrypting communications would decrease the chances of attackers to successfully leak data or steal credentials from other network components. By layering various security practices (segmentation and encryption, for example), the application will follow the defense-in-depth principle.

Note that using the http protocol is being deprecated by major web browsers.

In the past, it has led to the following vulnerabilities:

Ask Yourself Whether

There is a risk if you answered yes to any of those questions.

Recommended Secure Coding Practices

It is recommended to secure all transport channels (even local network) as it can take a single non secure connection to compromise an entire application or system.

Sensitive Code Example

url = "http://example.com" # Sensitive
url = "ftp://anonymous@example.com" # Sensitive
url = "telnet://anonymous@example.com" # Sensitive

import telnetlib
cnx = telnetlib.Telnet("towel.blinkenlights.nl") # Sensitive

import ftplib
cnx = ftplib.FTP("ftp.example.com") # Sensitive

import smtplib
smtp = smtplib.SMTP("smtp.example.com", port=587) # Sensitive

Compliant Solution

url = "https://example.com" # Compliant
url = "sftp://anonymous@example.com" # Compliant
url = "ssh://anonymous@example.com" # Compliant

import ftplib
cnx = ftplib.FTP_TLS("ftp.example.com") # Compliant

import smtplib
smtp = smtplib.SMTP("smtp.example.com", port=587) # Compliant
smtp.starttls(context=context)

smtp_ssl = smtplib.SMTP_SSL("smtp.gmail.com", port=465) # Compliant

Exceptions

No issue is reported for the following cases because they are not considered sensitive:

See